The present invention relates to a technology for
1. Field of the Invention setting a power supply voltage to be supplied to a microprocessor such as a CPU.
2. Description of the Related Art
A predetermined power supply voltage stabilized by a voltage regulator circuit (hereinafter referred to simply as “regulator circuit” also) is supplied to a microprocessor, such as a CPU, used in a personal computer, workstation, game device, or the like. The power supply voltage to be supplied to a microprocessor is set in accordance with a semiconductor fabrication process or the like employed for the microprocessor, and it is about 1.2 V for microprocessors fabricated by a low-voltage process of recent years.
Today a variety of microprocessors are being supplied by a plurality of vendors. The microprocessors supplied by the respective vendors specify power supply voltages to be supplied to themselves in their own schemes by the regulator circuits. In other words, the regulator circuits are designed such that they can accept the specification of a power supply voltage from a microprocessor. FIG. 8 is a block diagram showing an example of a conventional configuration of a microprocessor and a regulator circuit.
As shown in FIG. 8, a microprocessor 60 and a regulator 62 are parallely connected by a signal line 64 of 5 bits, for instance. The microprocessor 60 specifies a power supply voltage Vdd to be supplied to itself to the regulator circuit 62 by transmitting a VID (Voltage ID) signal through the signal line 64. The regulator circuit 62 produces the power supply voltage Vdd specified by the microprocessor 60 and supplies it to the microprocessor 60 through a power supply line 66. With such a configuration implemented, even when a user replaces the microprocessor 60 with another microprocessor 60, for instance, after the shipment of a device equipped with the microprocessor 60 and the regulator circuit 62 (hereinafter referred to simply as “set” also), an optimum power supply voltage Vdd can be supplied to the microprocessor 60 after the replacement.